If I keep a crayfish on black gravel, will he get more intense coloration or will he get more dark to blend in?

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What color is he? The coloring he has will likely get more intense. If he is blue or red for example he might be brighter. If he is grey he will probably just look darker grey.

I plan on getting a white one, a blue one, a black one, and a kinda cream one with some orange. The reason I asked was I want to know what color gravel I should get for them. The species are: Cherax destructor ---> white and blue morph, Cherax preissii ---> black, and Cherax holthuisi ---> kinda cream with some orange. I plan on buying them from Liveaquaria.com; Here's the link to the picture and crayfish: Freshwater Inverts and Amphibians: Freshwater Shrimp, Freshwater Snails, Frogs and Lobsters

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Don't forget crayfish will fight, even to the death, so if they are going to be in the same tank you'll need dividers or it has to be very big with a lot of decor.

How many crayfish would I be able to put in my tanks, if, say the 75 was 48 inches in length and 18 inches in depth(width) and my 125 was 72 inches in length and 18 in depth? The crayfish grow to about 12 inches in length.

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I think if all aquatic organisms were to go extinct, I'd go mad.<---I envision this as what I'd be doing!

Why that avatar? Visit: http://answers.yahoo.com/question/in...8040819AAz9c1R Read the best answer.

Some crayfish species will get darker if their surroundings, like gravel, are dark. I blogged about this on the Marmorkrebs blog, in a post called, "The curious case of crustacean colours."

Bowman investigated this in crayfish decades ago by placing crayfish in normal tanks, tanks painted black, and tanks painted white. Crayfish placed in black tanks had more red colouration, and those in the white tanks, more white colouration. Bowman also noted that animals that had become adapted to the bright white tanks did not darken up again after being placed into black surroundings. There are limits to how flexible the colour changes are.

Reference

Bowman TE. 1942. Morphological color change in the crayfish. The American Naturalist 76(764): 332-336.

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Department of Biology
The University of Texas-Pan American
Marmorkrebs.org